Differential Problesm on 2002 Ford Explorer

Car has 143,000 and is on 5th differential, a Ford limited slip and this one has gone 5 years. Started whining very loud 1000 miles ago. One mechanic looked at magnet plug and said diff is shot and just changed fluid. 2nd mechanic changed right rear wheel bearing, whine almost gone now, and said go ahead and drive it. Could shavings from a wheel bearing possibly get in the diff on this car? How many shavings are too many in this differential. Thanks, Georgeskiis